Transfusion of blood to someone who has suffered an injury or undergone a medical procedure resulting in blood loss is a well known and common practice. The transfused blood is typically donated by volunteers, and collected by organizations such as the International Red Cross, Magen David Adom, and private collection centers. Levels of blood donation are seasonal, dropping at certain times during the year, and are also affected by major events, such as the Sep. 11, 2001 attacks on the United States. After such well-publicized events, blood donations tend to soar, often irrespective of need (after the Sep. 11, 2001 attacks on the United States, for example, over half a million units were donated, while fewer than 300 were used for those injured in the attacks). Methods have been developed to store donated blood for future need.
Fresh Red Blood Cells (RBC) can be refrigerated for up to 42 days, after which they are discarded due to RBC recovery falling below 70% (for this reason, over 200,000 units of blood were discarded following the September 11 attacks). Frozen RBC units can be stored for up to 10 years.
During freezing of blood, the rate of cooling affects the morphology of the intracellular ice crystals. Maximizing the survival rate of RBCs requires careful control of the freezing process. Conventional freezing devices involve lowering the temperature of the chamber in a controlled stepped manner. The thermal gradient within the sample is determined implicitly by the temperature of the chamber and the thermal conductivity of the materials of the sample, and is not directly controllable.
U.S. Pat. No. 5,873,254 discloses a device for controlled freezing and warming of a biological sample, and freezing and thawing protocols for which the device is well suited. The device establishes a laterally varying thermal gradient and provides a mechanism for moving the sample along the thermal gradient at a controlled rate of speed. The sample is moved along the thermal gradient at a rate of speed that provides a variable cooling rate or a variable warming rate in accordance with the appropriate protocol. The device also allows continuous seeding of the sample through the freezing process at the exact freezing point of the solution. Real time monitoring and video imaging of the freezing process enable fine tuning of the thermodynamic parameters for improved control. However, the device is suited for small samples.
WO 03/056919 disclose a method for changing the temperature of a sample from an initial temperature via an intermediate temperature to a final temperature. Either the initial or the final temperatures is above the freezing point of said sample and the other is below the freezing point. The method is for changing the temperature of a sample having minimal dimension in each of two mutually perpendicular cross-sections exceeding 0.5 centimeters, and at least one of the cross-sections has an outer zone and an inner zone.